Over a million tractor-trailers transport goods and materials on U.S. highways at speeds of 55-75 mph, consuming fuel in the tens of billions of gallons per year and contributing to greenhouse gas emissions. Most of the fuel consumed at highway speeds is spent to overcome aerodynamic drag that occurs at the leading edge, trailing edge, and undercarriage of the tractor-trailer or other commercial motor vehicle (CMV). Aerodynamic hoods, gap fairings, and side trailer skirts have been deployed to reduce some of the drag. However, aerodynamic fairings have not been generally deployed at the rear end of such vehicles which typically have a blunt rear end with cargo doors. Also, commercial motor vehicles (CMV) such as passenger buses, vehicles carrying hazardous waste, and vehicles with gross weights of over 5 tons suffer from substantial rear end drag.
One solution to aft drag is the boat tail fairing, constructed of three or four flat panels hinging at the rear corners of a cargo door and angling in, rounding the rear end of the CMV and smoothing air flow somewhat. The back end of the fairing is generally open. However, a hinge and several stabilizer struts must be mounted to each cargo door, restricting access to the cargo door and complicating installation and use. The panels must be folded in for the cargo doors open toward the vehicle side surfaces. Additionally, the open/blunt end causes vortices and unresolved turbulence.
Another solution lowers aft turbulence via a closed-end pyramidal fairing made of panels angling inwardly. The panels are mounted to a frame attached by straps or hinging links to the top and bottom edges of the rear end. A scissors mechanism for holding the shape of an airflow surface may be folded and stowed for accessing the cargo door. In some cases, the entire fairing may be swung out from one side hinge to allow a cargo door to open against that side of the CMV. Unfortunately, the scissors mechanism is heavy and complex to fold and then stow. Additionally, door hinges may need to be replaced with wide-throw hinges to make room behind the cargo door for the folded fairing. Also, the amount of side clearance needed to swing the fairing toward the vehicle side surface is approximately the same as the trailer width, which is typically 102 inches.
Other solutions avoid complex mounting structures by frictionally attaching pyramidal or conical fairings to the rear end of the CMV. However, these fairings may require direct removal by more than one person, and may not be safely attached to the trailer. Additionally, snow and ice may accumulate on the flat surfaces and sharp corners of prior art fairings, making operation difficult or impossible due to obstruction, and potentially posing a hazard for other vehicles by dropping snow and ice onto the roadway.